Bio 180 Ch 55 (CSI) – Flashcards
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True or false? Species act as agents of natural selection when they interact.
answer
True
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What is niche differentiation?
a. the evolution of traits that reduce niche overlap and competition
b. interactions that allow species to occupy their fundamental niche
c. the degree to which the niches of two species overlap
d. the claim that species with the same niche cannot coexist
answer
a
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The relationship between ants and treehoppers in the presence of spiders is an example of
a. commensalism.
b. competition.
c. consumption.
d. mutualism.
answer
d
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What is one advantage of inducible defenses?
a. They are always present; thus, an individual is always able to
defend itself.
b. They make it impossible for a consumer to launch surprise
attacks.
c. They result from a coevolutionary arms race.
d. They make efficient use of resources, because they are produced
only when needed.
answer
d
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Pioneer species tend to have high _____ and lower survivorship.
answer
fecundity
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Which of these factors is not generally correlated with species diversity?
a. latitude
b. productivity
c. longitude
d. island size
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c
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The text claims that species interactions are conditional and dynamic. Do you agree with this statement? Why or why not? Cite specific examples to support your answer.
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Yes—the treehopper-ant mutualism is parasitic or mutualistic, depending on conditions; competition can evolve into no competition over time if niche dif- ferentiation occurs; arms races mean that the outcome of host-parasite interactions can change over time, and so forth (many other examples).
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Why does the phrase "coevolutionary arms race" appropriately characterize the long-term effects of species interactions?
a. Both plants and animals have evolved weapons for defense that
are so effective that many plants are not eaten, and predators
cannot reduce prey populations to extinction.
b. Adaptations that give one species a fitness advantage in an
interaction are likely to be countered by adaptations in the other
species that eliminate this advantage.
c. In all species interactions except for mutualism, at least one
species loses (suffers decreased fitness).
d. Even mutualistic interactions can become parasitic if conditions
change. As a result, interacting species are always "at war."
answer
b
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Biologists have tested the hypotheses that communities are highly predictable versus highly unpredictable. State the predictions
that these hypotheses make with respect to (a) changes in the distribution of the species in a particular community over time, and (b) the communities that should develop at sites where abiotic conditions are identical. Which hypothesis appears to be more accurate?
answer
(a) If community composition is predictable, then the species present should not change over time. But if composition is not predictable, then that species should undergo significant changes over time. (b) If community composition is predictable, then two sites with identical abiotic factors should develop identical communities.
If community composition is not predictable, then sites with identical abiotic factors should develop variable communities. In most tests, the data best match the predictions of the "not predictable" hypothesis, though communities show elements of both.
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What is a disturbance? Consider the role of fire in a forest. Compare and contrast the consequences of high-frequency versus low-frequency fire, and high versus low severity of fire.
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Disturbance is any short-lived event that changes the distribution of resources. Compared to low-frequency fires, high-frequency fires would tend to be less severe (less fuel builds up) and would tend to exert more intense natural selection for adaptations to resist the effects of fire. Compared to low-severity fires, high-severity fires would open up more space for pioneering species and would tend to exert more intense natural selection for adaptations to resist the effects of fire.
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Summarize the life-history attributes of early successional species. Why are these attributes considered adaptations?
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Early successional species are adapted to disperse to new environments (small seeds) and grow and reproduce quickly (reproduce at an early age, grow quickly). They can tolerate severe abiotic conditions (high temperature, low humidity, low nutrient availability) but have little competitive ability. These species are able to enter a new environment (with no competitors) and thrive. These attributes are considered adaptations because they in- crease the fitness of these species.
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Explain why high productivity should lead to increased species richness in habitats such as tropical rain forests and coral reefs.
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The idea is that high productivity will lead to high population den- sity of consumers, leading to competition and intense natural selection favoring niche differentiation that leads to speciation.
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Some insects harvest nectar by chewing through the wall of
the structure that holds the nectar. As a result, they obtain a nectar reward, but pollination does not occur. Suppose that you observed a certain bee species obtaining nectar in this way from a particular orchid species. Over time, how might you expect the characteristics of the orchid population to change in response to this bee behavior?
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Natural selection will favor orchid individu-
als that have traits that resist bee attack: thicker flower walls, nectar storage in a different position, a toxin in the flower walls, and so on. Individuals could also be favored if their anthers were in a position that accomplished pol- lination even if bees eat through the walls of the nectar- storage structure.
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You are a walking, talking community that includes trillions of bacterial and archaeal cells. Your gut, in particular, contains a complex microbial community. In some circumstances, the use of probiotics, which stimulate the rapid growth of bacteria that are mutalistic or commensal with humans, can eliminate the need to use antibiotics, which can wipe out helpful bacteria along with harmful bacteria. The use of probiotics is an example of which process?
a. succession
b. competitive exclusion
c. parasitism
d. niche differentiation
answer
b
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Suppose that a two-acre lawn on your college's campus is allowed to undergo succession. Describe how species traits, species interactions, and the site's history might affect the community that develops.
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The exact answer will depend on the location of the campus. The first species to appear must possess good dispersal ability, rapid growth, quick reproductive periods, and tolerance for very harsh and severe conditions. The two-acre plot is likely to be colonized first by pioneer species that have very "weedy" characteristics. But once colonization is under way, the course of succession will depend more on how the various species interact with each other.
The presence of one species can inhibit or facilitate
the arrival and establishment of another. For example, an early-arriving species might provide the shade and nutrients required by a late-arriving species. The site's history and nearby ecosystems may influence which spe- cies appear at each stage; for instance, an undisturbed ecosystem nearby could be a source for native species. The pattern and rate of this succession is also influenced by the overall environmental conditions affecting it. Only species with traits appropriate to the local climate are likely to colonize the site.
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Design an experiment to test the hypothesis that increasing species richness increases a community's productivity.
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One reasonable experiment would involve constructing artificial ponds and introducing different numbers of plankton species to different ponds, but the same total number of indi- viduals. (Any natural immigration to the ponds would have to be prevented.) After a period of time, remove all of the plankton and measure the biomass present. Make a graph with number of species on the x-axis and total biomass on the y-axis. If the hypothesis is correct, the line of best fit through the data should have a positive slope.
